yet Another First Robot (yAFRO)

So, here's my first robot (yAFRO)

It has nothing exceptional other than running on Arduino instead of PICaxe and being built form an old snakes and ladders board. I choosed this track geometry to make it different than the usuall Tamiya tank chassis. 

I still have much to do; the motor driver still doesn't work and I have to learn how to program the Arduino.

Since it's Arduino it can't be powered by only 4 AA batteries, do you have any good idea what type of battery I could use?

I chose not to use normal 9v batteries because I want something a bit more powerful, maybe 6 or 8 AA batteries, I don't know.

I'll update it when I have anything done.  Maybe even some videos if I have it running.

*CORRECTIONS, I changed AAA for AA, my error.*